Exhaust hoods which supply a substantial percentage of the air to the hood from a remote source, such as outside air, are shown in issued U.S. patents; for example, U.S. Pat. Nos. 3,457,850, 3,664,255 and 3,978,777. In these patents most of the air drawn through the hood is supplied from a source of outside air. By the use of such apparatus there is a great reduction in the demand for inside air to service the hood. In both hot and cold weather, such apparatus greatly reduces the load on the heating or cooling system of the building in which the hood is located.
It is important in devices of this character that the air injected into the hood from the remote source be directed substantially directly at the grease filter which typically intervenes between the air intake plenum and the air exhaust duct. In new construction, the direction of the air injected into the hood can be established by vanes and deflectors which will produce the desired angle of incidence of the injected air on the filter. However, when modifying an old hood installation which originally did not inject outside air into the hood, thus to adapt or convert such an old hood to utilize outside air as the major component of air drawn through the hood, it is difficult to prefabricate an air intake plenum air injection nozzle which will properly direct the air at the filter because the filter position and incline will vary from one installation to the next.
Moreover, the temperature of outside air drawn through the hood will vary during different seasons of the year. Accordingly, air density will vary from time to time and a nozzle which directs air on a proper path toward the filer at one time will not properly direct the air on a proper path toward the filter at a different time.
The devices of the prior art do not lend themselves to easy adjustment of the angle of incidence of air to the filter and are inadequate to accommodate for changes in seasons and utilization of a standard outside air injection nozzle with different existing hood installations.